This invention relates to an overdrive device for use in an automatic transmission of a vehicle such as an automobile.
More particularly, this invention relates to an overdrive device for an automatic transmission of the type incorporating a hydraulic torque converter disposed between an engine and a change gear mechanism. The conventional torque converter of an automatic transmission varies the turning force automatically and in a smooth and stepless fashion in accordance with the resistance of the vehicle. However, the conventional torque converter is severely limited in a practical sense because of considerable energy loss arising inevitably from fluid friction during the passage of fluid through the torque converter or from turbulence caused by a drastic change in the direction of flow of the fluid. Should a conventional overdrive device be employed in this type of automatic transmission, no satisfactory improvement in fuel efficiency can be attained because the engine power is transmitted automatically through the torque converter at the time of overdrive.
Accordingly, it is a primary object of this invention to provide a new overdrive device which eliminates the above-described problems of the conventional torque converter transmission.
It is a further object of this invention to provide an overdrive device which mechanically transmits the engine power to the change gear mechanism by not passing through the torque converter resulting in an improved fuel efficiency.
Another object of this invention is to minimize the fluctuations in the rotational force of the torque converter when not required. This usually occurs during a constant high speed operation of the engine for a long period such as in overdrive.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the overdrive device of this invention is for automatic transmission of the type including a change gear mechanism having an input shaft, and a torque converter having an input element connected to an engine and an output element connected to the shaft, and comprises means responsive to the operation of the change gear mechanism for connecting the shaft of the change gear mechanism to the input element of the torque converter thereby bypassing the output element of the torque converter.
Preferably, the overdrive device includes a planetary gear train having a sun gear, a carrier operatively responsive to the input element of the torque converter and a ring gear operatively connected to the shaft of the change gear mechanism. The overdrive device further includes overdrive brake means activated in response to the operation of the change gear mechanism for locking the sun gear against rotation whereby the ring gear is rotated by movement of the carrier in response to movement of the input element of the torque converter. A one-way clutch, normally connecting the output element of the torque converter to the shaft of the change gear mechansim, decouples the shaft from the output element when the speed of the shaft exceeds that of the output element of the torque converter.
The invention consists in the novel parts, constructions, arrangements, combinations and improvements shown and described. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the principles of the invention.